The analysis of a patient's urine sample for various substituents can be a powerful diagnostic tool for the detection of abnormal or disease states. For example, the determination of leukocyte concentration in urine serves as an indicator of urinary tract infection. Likewise, determination of other urine constituents such as ketone for diabetes mellitus, proteins for renal disease, nitrite for urinary tract infection and occult blood for damage to the kidneys or urinary tract is a useful diagnostic tool. The determination of physical characteristics such as the urine's specific gravity, which gives an indication of the kidney's ability to concentrate or dilute urine, and the clarity of the urine which is related to the presence or absence of white or red blood cells, epithelial cells or bacteria can be determined by measuring the urine sample's refractive index and/or clarity characteristics through an optical surface, i.e. a viewing port of acrylic or other transparent material such as glass.
Modern, automated urine analyzers, which can analyze several hundreds of urine samples in a normal day's operation and operate in a manner which brings the urine samples into direct contact with the optical surface, present a problem with the maintenance of the clarity of the optical surface since even a slight disruption in its clarity can introduce error into the determination of the physical property being measured. Exemplary of such automated urine analyzers are those in which specific gravity is determined by passing light through an omega shaped optic in which the light lost at the sharp bends is a function of the index of refraction of the medium of the surface of the fiber. The light that travels to the opposite end of the omega from the light source is measured and used to determine the specific gravity of the sample. Any substance with a different index of refraction that coats the fiber will change the sensitivity of the sensor. Accordingly, it is important that the optic be cleaned without leaving refractive index altering residue.
Cleaning of the optical surface in automated urine analyzers is typically accomplished by rinsing it with a cleaning solution between the application of each urine sample. One such cleaning formulation comprises a water solution of N,N-bis(2-hydroxyethyl)-N-methyl-9-octadecen-1-ammonium chloride. This solution, which is effective for dealing with the problem of false detection of leukocytes in negative urine samples that follow specimens that contain high levels of leukocytes, which problem is caused by the carry-over of leukocytes from sample to sample, has been found to be less than totally satisfactory because with intermittent rinsing, repeated contact of the optical surface with urine test samples tends to leave a residue on the surface which can distort the optical information which is transmitted therethrough.
It would be desirable and it is an object of the present invention to provide a cleaning solution for optical surfaces which come into repeated contact with urine test samples which solution is able to clean the surface in such a manner that the buildup of residue on the surface is avoided.